Maybe you can provide more information,
* when do you see this message ?
* perhaps include a screenshot [[How do I create a screenshot of my problem?]]
Have you tried using Firefox's safe mode does that prevent the messages appearing ?
* [[Troubleshoot Firefox issues using Safe Mode]]
(Not intended as a fix, just a first troubleshooting step)

Maybe you have some form of malware/adware or some odd toolbar inadvertently installed. It looks like Adblock plus has solved the problem for now.

In addition to a sceenshot of the problem looking at the error console may give some clue as to what is happening. (If you can reliably reproduce the problem after first clearing all the error messages)

use keyboard shortcut Ctrl + Shift + J

Maybe you have some form of malware/adware or some odd toolbar inadvertently installed. It looks like Adblock plus has solved the problem for now.
In addition to a sceenshot of the problem looking at the error console may give some clue as to what is happening. (If you can reliably reproduce the problem after first clearing all the error messages)
* use keyboard shortcut Ctrl + Shift + J